Two years ago, former NASA climate scientist James Hansen and a number of colleagues laid out a dire scenario in which gigantic pulses of fresh water from melting glaciers could upend the circulation of the oceans, leading to a world of fast-rising seas and even superstorms.
Hansen's scenario was based on a computer simulation, not hard data from the real world, and met with skepticism from a number of other climate scientists.
But now, a new oceanographic study appears to have confirmed one aspect of this picture - in its early stages, at least.
The new research, based on ocean measurements off the coast of East Antarctica, shows that melting Antarctic glaciers are indeed freshening the ocean around them.
And this, in turn, is blocking a process in which cold and salty ocean water sinks below the sea surface in winter, forming "the densest water on the Earth," in the words of study lead author Alessandro Silvano, a researcher with the University of Tasmania in Hobart, Australia.
This so-called Antarctic bottom water has stopped forming in two key regions of Antarctica, the research shows - the West Antarctic coast and the coast around the enormous Totten glacier in East Antarctica.
These are two of Antarctica's fastest-melting regions, and no wonder: When cold surface water no longer sinks into the depths, a deeper layer of warm ocean water can travel across the continental shelf and reach the bases of glaciers, retaining its heat as the cold waters remain above.
This warmer water then rapidly melts the glaciers and the large floating ice shelves connected to them.
In other words, the melting of Antarctica's glaciers appears to be triggering a "feedback" loop in which that melting, through its effect on the oceans, triggers still more melting.
The melting water stratifies the ocean column, with cold fresh water trapped at the surface and warmer water sitting below Then, the lower layer melts glaciers and creates still more melt water - not to mention rising seas as glaciers lose mass.
"What we found is not only a modeling study but is something that we observed in the real ocean," said Silvano, who conducted the research in Science Advances with colleagues from several other institutions in Australia and Japan.
"Our study shows for the first time actual evidence of this mechanism. Our study shows that it is already happening."
Hansen said that "this study provides a nice small-scale example of processes that we talk about in our paper."
"On the large-scale issue, it is too early to say how these feedback processes will play out, based on empirical evidence," Hansen said by email.
"If we stay on business-as-usual [greenhouse gas] emissions rates, so that global warming continues to increase, I expect that the freshwater injection rate will increase (mainly via ice faster ice shelf breakup and underwater melt) and sea ice area will increase. This experiment will be playing out over the next years and decades."
According to Matthew Long, an oceanographer at the National Center for Atmospheric Research, the study "is consistent with a large body of existing literature that shows warming and freshening of the deep ocean in the southern hemisphere"
"The fact that we see consistent warming and freshening indicates that the processes we expect to play out over the next century are already underway," Long said.
"Indeed, this study is part of a growing body of evidence suggesting that the world's oceans are changing - and that the pace of change is beginning to accelerate."
If the process of Antarctic bottom water formation is being impaired, at least in some regions, then it would be a Southern hemisphere analogue of a process that has already caused great worry and drawn considerably more attention - a potential slowdown of the overturning circulation in the North Atlantic Ocean, thanks to freshening of the ocean from the melting of Greenland.